1. Field of the Invention
The present invention relates to a method of high-power-density beam welding in combination with upset welding for metal plates, sheets and wires, or formed or machined articles made therefrom, and an apparatus for performing the method.
2. Description of the Related Art
Conventionally, upset resistance welding methods such as upset welding and flash welding, or high-power-density beam welding methods using laser, electron beam, etc. have often been used to join metal plates, sheets and wires, especially those of relatively small thickness or diameter.
The upset welding method comprises clamping two parts to be welded to each other on a fixed electrode and a movable electrode, respectively, advancing the movable electrode toward the fixed electrode to upset the abutting edges of the parts against each other, and supplying an electric current to the parts while causing a predetermined upsetting pressure on the abutting edges thereof. The heat produced within the parts by the resistances of the parts and the contact resistances of the abutting faces thereof will produce plastic deformations in the parts and weld the parts to each other.
The flash welding method is performed using the same welding steps and with the same arrangement as in the above-described upset welding method, except that flashes are produced between the parts during the welding process to assure heating with higher efficiency.
These resistance welding methods present great merits in economy such as elimination of filler metal, a high efficiency due to a short welding time, and do not require high accuracy in the machining of the abutting edges of the parts to be joined.
In addition, these methods present the advantage that the entire area of the abutting surface of the parts are joined to each other simultaneously, so that distortions due to the temperature gradient of the weld are smaller than those caused by arc or beam welding, where the edges of the parts are welded to each other along the weld line sequentially by moving from one extremity thereof to the other.
For comparison between flash welding and upset welding, the former is feasible even if the edge machining is relatively rough, while the latter is more suited for automation of a welding line which requires a clean working environment, because it produces no flash during the welding process.
Upset welding methods are described, for example, in the Japanese Laid-Open Patent Applications No. Sho 61-38787 and No. Sho 61-38788.
The high-power-density beam welding method comprises directing a laser beam or high-power-density electron beam onto abutting edges of parts to be joined to fuse and weld the abutting edges. This welding method has been widely practiced, because it presents great technical and economical merits. The use of a concentrated heat source with a high energy density results in narrower heated and fused areas of the parts members and narrower areas of the parts in which the material properties are chanced and geometrical deformation is caused
Despite the above advantages, the upset welding methods present the follwing disadvantages:
(1) They require a large amount of electric power for heating and a high mechanical force for welding pressure;
(2) Excess metal formed at the interface of the abutting edges must be trimmed after welding. This trimming requires an additional step and results in increased losses of welded products causing a lowered yield;
(3) Defects such as oxide slag, insufficient heat and defects due to the upsetting pressure are liable to be left in joined interfaces, especially in the welded edge portion of the parts. Since there is no applicable non-destructive inspection method for these defects, the consistency of product quality must be assured by relying on a random sampling with destructive inspection. Therefore, the quality guarantee control cost is increased, especially for products which require high reliability.
The high-power-density beam welding method presents the following disadvantages;
(1) The use of concentrated heat source requires a high accuracy in work piece alignment and consequently a large amount of labor for edge preparation. To solve these problems, a method wherein a preliminary welding is performed before the main welding is irradiation of high-power-density beam is disclosed in the Japanese Laid-Open Patent Application No. Sho 57-160582.
(2) The quick heating and quick cooling of welded objects leads to excessive hardening and undesirable changes in material properties.
(3) Any shortage of filler metal tends to produce defects in weld bead formation, such as lack of weld metal produced at the edge portions of a welded parts at the finishing points of welding, as well as undercuts and collapses in weld sections, which cannot be repaired after the completion of welding, or may adversely affect the mechanical strength of welded objects.
The Japanese Laid-Open Patent Application No. Sho 57-202985discloses an electric welding method wherein an electric contact is effected by laser irradiation first and then resistance Joule heating is caused by electric conduction. This method is intended to weld two materials which are remarkably different in their heat capacity.